Parallel interconnection of neighboring solar cells with dual common back planes

ABSTRACT

A solar assembly or module comprising a plurality of solar cells and a support, the support comprising a conductive layer or back plane on each planar side. Each one of the plurality of solar cells is placed on the first conductive portion with the first contact electrically connected to the first conductive portion so that the solar cells are connected in parallel through the first conductive portion. A second contact of each solar cell can be connected to the second conductive portion so that the first and second conductive portions form terminals of opposite conductivity type. The modules can be interconnected to form a string or an electrical series connection of discrete modules by overlapping and bonding the first terminal of a first module with the second terminal of a second module.

REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/719,111 filed May 21, 2015, which is a continuation-in-partof U.S. patent application Ser. No. 14/592,519 filed Jan. 8, 2015, whichclaims the benefit of U.S. Provisional Patent Application No. 61/976,108filed Apr. 7, 2014.

BACKGROUND OF THE DISCLOSURE 1. Field of the Invention

The present invention relates to the field of photoelectric solar cellarrays, and to fabrication processes utilizing, for examplemultijunction solar cells based on III-V semiconductor compoundsfabricated into multi-cell modules or subassemblies of such solar cells,and an automated process for mounting and interconnection of suchsubassemblies on a substrate or panel.

2. Description of the Related Art

Solar power from photovoltaic cells, also called solar cells, has beenpredominantly provided by silicon semiconductor technology. In the pastseveral years, however, high-volume manufacturing of III-V compoundsemiconductor multijunction solar cells for space applications hasaccelerated the development of such technology not only for use in spacebut also for terrestrial solar power applications. Compared to silicon,III-V compound semiconductor multijunction devices have greater energyconversion efficiencies and generally more radiation resistance,although they tend to be more complex to manufacture. Typical commercialIII-V compound semiconductor multijunction solar cells have energyefficiencies that exceed 27% under one sun, air mass 0 (AM0),illumination, whereas even the most efficient silicon technologiesgenerally reach only about 18% efficiency under comparable conditions.Under high solar concentration (e.g., 500×), commercially availableIII-V compound semiconductor multijunction solar cells in terrestrialapplications (at AM1.5D) have energy efficiencies that exceed 37%. Thehigher conversion efficiency of III-V compound semiconductor solar cellscompared to silicon solar cells is in part based on the ability toachieve spectral splitting of the incident radiation through the use ofa plurality of photovoltaic regions with different band gap energies,and accumulating the current from each of the regions.

Typical III-V compound semiconductor solar cells are fabricated on asemiconductor wafer in vertical, multijunction structures. Theindividual solar cells or wafers are then disposed in horizontal arrays,with the individual solar cells connected together in an electricalseries circuit. The shape and structure of an array, as well as thenumber of cells it contains, are determined in part by the desiredoutput voltage and current.

In satellite and other space related applications, the size, mass andcost of a space vehicle or satellite power system are dependent on thepower and energy conversion efficiency of the solar cells used. Puttingit another way, the size of the payload and the availability of on-boardservices are proportional to the amount of power provided. Thus, aspayloads become more sophisticated and require more power, both thepower-to-weight ratio (measured in watts per kg) and power-to-area ratio(measured in watts per square meter) of a solar cell array or panelbecomes increasingly more important, and there is increasing interest inlighter weight, densely packed solar cell arrays having both highefficiency and low mass.

Space applications frequently use high efficiency multijunction III/Vcompound semiconductor solar cells. Compound semiconductor solar cellwafers are often costly to produce. Thus, the waste that hasconventionally been accepted in the art when cutting the rectangularsolar cell out of the substantially circular solar cell wafer, can implyconsiderable cost.

Solar cells are often produced from circular or substantially circularwafers sometimes 100 mm or 150 mm in diameter. Large solar cells (i.e.with, for example, an area from 25 to 60 cm² representing one-quarter ormore of the area of the wafer) are conventionally preferred so as tominimize the costs associated with the assembly of the solar cells ontoa support to form a solar cell module. However, the use of large solarcells results in poor wafer utilization, and large solar cells oftenpresent issues of defects or variation in the material quality acrossthe surface of the wafer. Also, larger solar cells are fragile andpresent handling challenges during subsequent fabrication steps thatresult in breakage of the wafer or solar cells and corresponding lowermanufacturing yield. Moreover, large solar cells of predetermined sizecannot be easily or efficiently accommodated on panels of arbitraryaspect ratios and configurations which may vary depending upon the“wing” configuration of the satellite or space vehicle. Also, largesolar cells are rigid and can sometimes be problematic in terms ofmeeting requirements for flexibility of the solar cell assembly or solararray panel. Sometimes, flexibility is desired so that the solar cellassembly or the solar array panel can be bent or rolled, for example, sothat it is displaceable between a stowed position in which it is woundaround a mandrel or similar, and a deployed position extending outwardfrom, for example, a space vehicle so as to permit the solar cells toreceive sunlight over a substantial area. Sometimes, large solar cellscan be problematic from the perspective of providing a flexible assemblyor panel that can be readily bent, wound, etc. without damage to thesolar cells and their interconnections.

It is possible to reduce the amount of waste by dividing a circular orsubstantially circular wafer not into one or two single cells, but intoa large number of smaller cells. By dividing a circular or substantiallycircular wafer into a large amount of relatively small cells, most ofthe wafer surface can be used to produce solar cells, and the waste isreduced. For example, a solar cell wafer having a diameter of 100 mm or150 mm and a surface area in the order of 80 cm² or 180 cm² can be usedto produce a large amount of small solar cells, such as square orrectangular solar cells, each having a surface area of less than 5 cm²,or in some embodiments less than 1 cm², less than 0.1 cm², less than0.05 cm², or less than 0.01 cm². For example, substantiallyrectangular—such as square—solar cells can be obtained in which thesides are less than 10, 5, 3, 2, 1 or even 0.5 mm long. Thereby, theamount of waste of wafer material can be substantially reduced, and atthe same time high utilization of the wafer surface can be obtained.Also, when dividing a solar cell wafer into a relatively large number ofsolar cells, solar cells obtained from a more or less defective regionof the wafer can be discarded, or “binned” as lower performance solarcells, that is, not used for the manufacture of the solar cellassemblies. Thus, a relatively high quality of the solar cell assembliesin terms of performance of the solar cells can be achieved, while theamount of waste is kept relatively low.

However, the use of a large number of relatively small solar cellinvolves the drawback that for a given effective surface area of thefinal solar cell assembly or solar array panel, there is an increasednumber of interconnections between solar cells, in a parallel and/or inseries, which may render the process of manufacturing the solar cellassembly or the panel more complex and/or expensive, and which may alsorender the entire circuit less reliable, due to the risk for lowreliability, low yield, or other manufacturing difficulties or errorsdue to defective or less-than-ideal interconnections between individualsolar cells.

SUMMARY OF THE DISCLOSURE 1. Objects of the Disclosure

It is an object of the present invention to provide an improvedmultijunction solar cell assembly or module comprising a plurality ofsolar cells.

It is an object of the present invention to provide a platform orsubstrate for the series and/or parallel connection of discrete groupsof solar cells.

It is an object of the present invention to provide a lightweight solarcell assembly or module that is suitable for automated manufacturingprocesses.

It is another object of the invention to provide a flexible solar cellarray module with high W/kg and W/m² and low cost.

It is another object of the invention to provide a solar cell assemblyor module that utilizes an array of small solar cells, for example,solar cells each having a surface area of less than 5 cm², or in someembodiments less than 1 cm², less than 0.1 cm², less than 0.05 cm², orless than 0.01 cm², for example, substantially rectangular—such assquare—solar cells in which the (longest) sides are less than 10, 5, 3,2, 1 or even 0.5 mm long.

It is another object of the invention to provide for methods forproducing solar cell assemblies or modules.

It is another object of the invention to provide for a solar array panelcomprising a plurality of interconnected modules, and methods forproducing a solar array panel.

Some implementations or embodiments may achieve fewer than all of theforegoing objects.

2. Features of the Disclosure

Briefly, and in general terms, the present disclosure relates to amodular solar assembly comprising a support comprising a first side andan opposing second side; a first conductive layer comprising a firstconductive portion disposed on the first side of the support; a secondconductive layer comprising a second conductive portion disposed on thesecond side of the support; a plurality of solar cells mounted on thefirst side of the support, each solar cell of the plurality of solarcells comprising a top surface including a contact of a first polaritytype, such as a cathode contact, and a rear surface including a contactof a second polarity type, such as an anode contact; the contact of thesecond polarity type of each of the plurality of solar cells makingelectrical contact with the first conductive portion of the firstconductive layer; a plurality of vias in the support extending from thefirst side of the support to the second conductive portion on the secondside of the second support; a plurality of conductive interconnectsextending from the first side of the support to the second conductiveportion on the second side of the support, each respective interconnectmaking electrical contact with the contact of the first polarity type ofa respective solar cell and extending through a respective via to makeelectrical contact with the second conductive portion of the secondconductive layer disposed on the second side of the support; a firstterminal of the module disposed on the second side of the support andconnected to the second conductive portion; and a second terminal of themodule disposed on the first side of the support and connected to thefirst conductive portion.

In some embodiments of the disclosure, the second terminal comprises oris made up of part of the first conductive layer, and the first terminalcomprises or is made up of part of the second conductive layer.

In some embodiments the assembly further comprises a bypass diode whichcan be mounted on, for example, any of the first and second surfaces andfunction as a bypass diode for the entire solar cell assembly orsubportions or groups of solar cells thereof. Bypass diodes arefrequently used in solar cell assemblies comprising a plurality ofseries connected solar cells or groups of solar cells. One reason forthe use of bypass diodes is that if one of the solar cells or groups ofsolar cells is shaded or damaged, current produced by other solar cells,such as by unshaded or undamaged solar cells or groups of solar cells,can flow through the by-pass diode and thus avoid the high resistance ofthe shaded or damaged solar cell or group of solar cells. The bypassdiodes can be mounted on one of the metal layers and comprise an anodeterminal and a cathode terminal. The diode can be electrically coupledin parallel with the semiconductor solar cells and configured to bereverse-biased when the semiconductor solar cells generate an outputvoltage at or above a threshold voltage, and configured to beforward-biased when the semiconductor solar cells generate an outputvoltage below the threshold voltage. Thus, when the solar cell assemblyis connected in series with other solar cell assemblies, the bypassdiode can serve to minimize the deterioration of performance of theentire string of solar cell assemblies when one of the solar cellassemblies is damaged or shaded.

In another aspect, the present disclosure provides a modular solar cellassembly and its method of fabrication comprising a support comprising afirst side and an opposing second side; a first conductive layercomprising a first conductive portion disposed on the first side of thesupport, a second conductive layer comprising a second conductiveportion disposed on the second side of the support.

In some embodiments, a plurality of solar cells are mounted on the firstside of the support, each solar cell of the plurality of solar cellscomprising a top surface including a contact of a first polarity type(such as a cathode contact in embodiments in which the solar cell is ann-on-p configuration), and a rear surface including a contact of asecond polarity type (such as an anode contact in embodiments in whichthe solar cell is an n-on-p configuration); the contact of secondpolarity type of each of the plurality of solar cells making electricalcontact with the first conductive portion of the first conductive layer.

In some embodiments, a plurality of vias in the support are providedextending from the first side of the support to the second side of thesupport, and a plurality of conductive interconnects are providedextending from the first side of the support to the second side of thesupport, each respective interconnect making electrical contact with thecontact of the first polarity type of a respective solar cell andextending through a respective via to make electrical contact with thesecond conductive layer disposed on the second side of the support.

In some embodiments, a first terminal of the module is disposed on thesecond side of the support and connected to the second conductiveportion; and a second terminal of the module is disposed on the firstside of the support and connected to the first conductive portion.

In some embodiments, the first conductive portion comprises a pluralityof parallel strips of equal width. In other embodiments of theinvention, the first conductive portion comprises a plurality of stripshaving a width that varies along the strip, for example, a width thatincreases from a free end of the strip to an end of the strip where thestrip is electrically connected to the second terminal. For example, thestrips can have a substantially triangular configuration.

In some embodiments, the second conductive portion comprises a planarsurface covering the entire rear surface of the support, or a pluralityof parallel strips on the rear surface. In other embodiments of theinvention, the second conductive portion comprises a plurality of stripshaving a width that varies along the strip, for example, a width thatincreases from a free end of the strip to an end of the strip where thestrip is electrically connected to the first terminal. For example, thestrips can have a substantially triangular configuration.

A reason for the use of strips having a width that varies along thestrip on either the top or the rear surface is that when current flowsin one direction, such as from a free end of the strip towards an end ofthe strip where the strip is connected to the terminal, the amount ofcurrent increases along the strip, as more and more solar cells mountedon the strip are connected in electrical series, and contribute to thetotal current flowing in the strip. Thus, the closer one gets to the endof the strip where the strip is connected to the terminal, the higherthe need for a substantial cross section of the conductive material inorder to carry the current and avoid overheating or excessive losses.Thus, varying the width of the strips and thus the cross sectional areaof the conductive material in accordance with the increase in current,optimizes the use of conductive material and thus implies a saving interms of weight, which is important especially in space applications.

In some embodiments, the first conductive portion is a metallic layerthat has a thickness in the range of 5 to 50 microns.

In some embodiments, a plurality of solar cells are disposed closelyadjacent to one another on each of the strips by a distance between 5and 25 microns.

In some embodiments, each of the solar cells have a dimension in therange of 0.5 to 10 mm on a side

In some embodiments, the support is a polyimide film having a thicknessof between 25 and 100 microns.

In some embodiments, the via has a diameter of between 100 and 200microns.

In some embodiments, the first terminal of the module is disposed on afirst peripheral edge of the module.

In some embodiments, the second terminal of the module is composed of ametallic strip extending parallel to the first peripheral edge of themodule.

In some embodiments of the disclosure, the first terminal and the secondterminal are arranged in correspondence with opposite peripheral edgesof the support.

The arrangement of the present disclosure makes it possible to connect aplurality of assemblies in series by arranging the assemblies one afterthe other in a partly overlapping manner, for example, in a way similarto the way in which roofing tiles are arranged on a roof, so that thesecond terminal of one of the assemblies contacts the first terminal ofanother one of the assemblies. This provides for easy electrical andmechanical interconnection without any use of discrete, complexinterconnect elements, and the laborious welding or soldering of theinterconnect elements to the terminals. The terminals of adjacentassemblies can be directly placed in contact with each other andattached using suitable bonding means, such as soldering or welding.

In some embodiments, the bypass diode has a top terminal of a firstpolarity type and a bottom terminal of a second polarity type, and thebottom terminal is mounted on and electrically connected to the firstconductive layer.

In some embodiments of the disclosure, at least the first conductiveportion comprises a plurality of strips, wherein said vias are arrangedbetween adjacent strips. The solar cells can thus be arranged on thestrips, for example, with one or two rows of solar cells on each strip,and interconnects such as simple wires, such as wire bonded wires, canpass from the solar cells to the second conductive portion through viasarranged in rows parallel with said rows of solar cells, and arrangedbetween the strips. In some embodiments of the disclosure, the stripshave one free end and another end where the strips are connected to theterminal.

In some embodiments, the assembly is an array of between 9 and 36 solarcells.

In some embodiments, the solar cells are multijunction III/V compoundsemiconductor solar cells.

It has been found that this arrangement is practical and appropriate forautomated manufacturing processes. The solar cells can be tightly packedadjacent to one another at one side of the support, whereas the otherside of the support is used as a conductive backplane to provide anelectrical element that connects some or all of the solar cells inparallel. Also, the presence of terminals on both sides of the supportfacilitates interconnection and integration of the assemblies or modulesinto a solar array panel in a simply and highly ordinated manner andwithout need for special or discrete interconnects between the differentmodules. For example, a series of said solar cell modules or assembliescan be arranged in a row with the second terminal of one of the solarcell modules overlapping with and being bonded to the first terminal ofa preceding solar cell module, etc. Thus, a simple and reliablemechanical and electrical series connection of solar cell modules can beestablished.

In another aspect, the present disclosure provides a solar array panelcomprising a plurality of modular solar cell assemblies, each solar cellassembly including an interconnect which electrically and mechanicallyconnects to the solar cell assembly with an adjacent solar cellassembly, and wherein each solar cell assembly includes a supportcomprising a first side and an opposing second side; a first conductivelayer comprising a first conductive portion disposed on the first sideof the support, a second conductive layer comprising a second conductiveportion disposed on the second side of the support, a plurality of solarcells mounted on the first side of the support, each solar cell of theplurality of solar cells comprising a top surface including a contact ofa first polarity type, and a rear surface including a contact of asecond polarity type, the contact of second polarity type of each of theplurality of solar cells making electrical contact with the firstconductive portion of the first conductive layer; a plurality of vias inthe support extending from the first side of the support to the secondside of the support; a plurality of conductive interconnects extendingfrom the first side of the support to the second side of the support,each respective interconnect making electrical contact with the contactof the first polarity type of a respective solar cell and extendingthrough a respective via to make electrical contact with the secondconductive layer disposed on the second side of the support; a firstterminal of the module disposed on the second side of the support andconnected to the second conductive portion; and a second terminal of themodule disposed on the first side of the support and connected to thefirst conductive portion.

In another aspect, the present disclosure provides a space vehicle andits method of fabrication comprising: a payload disposed on or withinthe space vehicle; and a power source for the payload, including anarray of solar cell assemblies mounted on a panel, each solar cellassembly including a support comprising a first side and an opposingsecond side; a first conductive layer comprising a first conductiveportion disposed on the first side of the support; a second conductivelayer comprising a second conductive portion disposed on the second sideof the support; a plurality of solar cells mounted on the first side ofthe support, each solar cell of the plurality of solar cells comprisinga top surface including a contact of a first polarity type, and a rearsurface including a contact of a second polarity type, the contact ofsecond polarity type of each of the plurality of solar cells makingelectrical contact with the first conductive portion of the firstconductive layer; a plurality of vias in the support extending from thefirst side of the support in a direction to the second side of thesupport; a plurality of conductive interconnects extending from thefirst side of the support in a direction to the second side of thesupport, each respective interconnect making electrical contact with thecontact of first polarity type of a respective solar cell and extendingthrough a respective via to make electrical contact with the secondconductive layer disposed on the second side of the support, a firstterminal of the module disposed on the second side of the support andconnected to the second conductive portion; and a second terminal of themodule disposed on the first side of the support and connected to thefirst conductive portion.

In another aspect, the present disclosure provides a solar cell assemblythat comprises a plurality of solar cells and a support, the supportcomprising a conductive layer, such as a metal layer, comprising a firstconductive portion. Each solar cell of said plurality of solar cellscomprises a top or front surface and a bottom or rear surface and abottom contact in correspondence with said rear surface. Each solar cellis placed on the first conductive portion with the bottom contactelectrically connected to the first conductive portion so that theplurality of solar cells are connected in parallel through the firstconductive portion. In the present disclosure, the term solar cellrefers to a discrete solar cell semiconductor device or chip.

In another aspect, the present disclosure provides a method ofmanufacturing a solar cell assembly having between 16 and 100 solarcells, in which the solar cells are positioned and placed on a supportin an automated manner by a pick and place assembly tool.

In another aspect, the present disclosure provides a method ofmanufacturing a solar cell assembly having between 16 and 100 solarcells, in which the solar cells are positioned and placed on a firstconductive portion of a support, so that the solar cells can make up asubstantial part of the upper surface of the support, such as more than50%, 70%, 80%, 90%, 95% or more of the total surface of the support.

In another aspect, the present disclosure provides a method ofmanufacturing a solar cell assembly having between 16 and 100 solarcells, in which the solar cells are positioned and placed on aconductive portion of a support, so that the contact or contacts at therear surface of each solar cell are electrically connected, which thusserves to interconnect the solar cells in parallel.

In some embodiments, the connection between the bottom contact of eachsolar cell and the first conductive portion of the metal layer of thesupport can be direct and/or through a conductive bonding material.Thus, this approach is practical for creating solar cell assemblies of alarge amount of relatively small solar cells, such as solar cellsobtained by dividing a solar cell wafer having a substantially circularshape into a large number of individual solar cells having asubstantially rectangular shape, for enhanced wafer utilization. Thefirst conductive portion is continuous and thus acts as a businterconnecting the bottom contacts of the solar cells. In addition, theconductive layer, including the first conductive portion, can act as athermal sink for the solar cells.

In some embodiments of the disclosure, the conductive layer comprises asecond conductive portion of a second conductivity type separated fromthe first conductive portion of a first conductivity type, that is, thetwo conductive portions are not in direct contact with each other. Forexample, the two conductive portions can be arranged on different sidesof an insulating support or core. Each of the plurality of solar cellscomprises a top contact of a first conductivity type, and each of theplurality of solar cells is connected to the second conductive portionvia the top contact by an interconnect connecting the top contact to thesecond conductive portion. Thus, a plurality of solar cells can bearranged on the support, connected in parallel with each other, withtheir bottom contacts (such as contacts coupled to a p-polarity side ofthe respective solar cell in some embodiments) connected to the firstconductive portion and with their top contacts (such as contacts coupledto an n-polarity side of the respective solar cell) connected to thesecond conductive portion. The first and second conductive portions canserve as bus-bars allowing the connection of the solar cell assembly toother devices, such as to the other solar cell assemblies so as to makeup a larger solar cell assembly.

In some embodiments of the disclosure, the first conductive portion andthe second conductive portion are interconnected by means of at leastone bypass diode. A bypass diode functions for routing electricalcurrent around the solar cells. Bypass diodes are frequently used insolar cell assemblies comprising a plurality of series connected solarcells or groups of solar cells. If one of the solar cells or groups ofsolar cells is shaded or damaged, current produced by other solar cells,such as by unshaded or undamaged solar cells or groups of solar cells,can flow through the bypass diode and thus avoid the high resistance ofthe shaded or damaged solar cell or group of solar cells. The diodes canbe mounted on the top side of the metal layer and comprise an anodeterminal and a cathode terminal, with one terminal connected to themetal layer. The diode can be electrically coupled in parallel with thesemiconductor solar cells and configured to be reverse-biased when thesemiconductor solar cells generate an output voltage at or above athreshold voltage, and configured to be forward-biased when thesemiconductor solar cells generate an output voltage below the thresholdvoltage.

In some embodiments of the disclosure, said at least one diode comprisesa top side terminal and a rear side terminal, the diode being placed onthe second conductive portion with said rear side terminal of the diodeelectrically coupled to the second conductive portion, the top sideterminal of the diode being electrically coupled to the first conductiveportion, for example, through a via in a support or core separating thefirst conductive portion from the second conductive portion. In analternative embodiment of the disclosure, the diode can be placed on thefirst conductive portion with the rear side terminal of the diode beingelectrically coupled to the first conductive portion, the top sideterminal of the diode being electrically coupled to the secondconductive portion. Both alternatives are possible, but it may sometimesbe preferred to use the first conductive portion to support the solarcells, and the second conductive portion to support the diode or diodes.In other embodiments, it can be preferred to have both the diode and thesolar cells arranged on the same conductive portion, for example, on thesame side of a support having the first conductive portion on one sideand the second conductive portion on another side. Having all the solarcell and diode components on the same side of the support may sometimesserve to simplify the assembly process.

In some embodiments of the disclosure, the solar cell assembly comprisesa plurality of rows of solar cells placed on the first conductiveportion, each row of solar cells being connected to a subportion, suchas a strip, of the second conductive portion, through vias arranged inrows extending in parallel with the solar cells.

In some embodiments of the disclosure, each solar cell has a surfacearea of less than 1 cm². The approach of the disclosure can beespecially advantageous in the case of relatively small solar cells,such as solar cells having a surface area of less than 1 cm², less than0.1 cm² or even less than 0.05 cm² or 0.01 cm². For example,substantially rectangular—such as square—solar cells can be obtained inwhich the sides are less than 10, 5, 3, 2, 1 or even 0.5 mm long. Thismakes it possible to obtain rectangular solar cells out of asubstantially circular wafer with reduced waste of wafer material, andthe approach of the disclosure makes it possible to easily place andinterconnect a large number of said solar cells in a parallel, so thatthey, in combination, perform as a larger solar cell.

In some embodiments of the disclosure, each solar cell is bonded to thefirst conductive portion by a conductive bonding material. Using aconductive bonding material makes it possible to establish theconnection between a bottom contact of each solar cell and the supportby simply bonding the solar cell to the support using the conductivebonding material. The conductive bonding material can be selected toenhance heat transfer between solar cell and support.

In some embodiments of the disclosure, the conductive bonding materialis an indium alloy. Indium alloys have been found to be useful andadvantageous, in that the indium can make the bonding material ductile,thereby allowing the use of the bonding material spread over asubstantial part of the surface of the support without making thesupport substantially more rigid and reducing the risk of formation ofcracks when the assembly is subjected to bending forces. Preferably,support, solar cells and bonding material are matched to each other tofeature, for example, similar thermal expansion characteristics. On theother hand, the use of a metal alloy, such as an indium alloy, isadvantageous over other bonding material such as polymeric adhesives inthat it allows for efficient heat dissipation into the underlyingconductive layer, such as for example a copper layer. In someembodiments of the disclosure, the bonding material is indium lead.

In some embodiments of the disclosure, the conductive layer comprisescopper.

In some embodiments of the disclosure, the support comprises a KAPTON®film, the conductive layer being placed on the KAPTON® film. The optionof using a KAPTON® film for the support is practical for, for example,space applications.

In some embodiments of the disclosure, the contact of the secondpolarity type of each solar cell comprises a conductive, such as ametal, layer extending over a substantial portion of the rear surface ofthe respective solar cell, preferably over more than 50% of the rearsurface of the respective solar cell, more preferably over more than 90%of the rear surface of the respective solar cell. In some embodiments ofthe disclosure, the contact of the second polarity type comprises aconductive, such as a metal, layer covering the entire rear surface ofthe solar cell. This helps to establish a good and reliable contact withthe conductive portion of the conductive layer of the support.

In some embodiments of the disclosure, each solar cell comprises atleast one III-V compound semiconductor layer. As indicated above, highwafer utilization can be especially advantageous when the solar cellsare high efficiency solar cells such as III-V compound semiconductorsolar cells, often implying the use of relatively expensive wafermaterial.

In some embodiments of the disclosure, the solar cell assembly has asubstantially rectangular shape and a surface area in the range of 25 to400 cm².

Another aspect of the disclosure relates to a solar array panelcomprising a plurality of solar cell assemblies, each of these solarcell assemblies comprising a solar cell assembly according to one of thepreviously described aspects of the disclosure. As indicated above, thesolar cell assemblies can advantageously serve as sub-assemblies whichcan be interconnected to form a major solar array panel, comprising, forexample, an array of solar cell assemblies comprising a plurality ofstrings of such solar cell assemblies, each string comprising aplurality of solar cell assemblies connected in series. Thus, a modularapproach can be used for the manufacture of relatively large solar arraypanels out of small solar cells, which are assembled to form assembliesas described above, whereafter the assemblies or modules areinterconnected to form a panel.

In some embodiments of the disclosure, the step of providing a pluralityof solar cells comprises obtaining a plurality of substantiallyrectangular solar cells, such as square solar cells, out of asubstantially circular wafer. In some embodiments of the disclosure,each of said solar cells has a surface area of less than 1 cm². Theapproach of the disclosure can be especially advantageous in the case ofrelatively small solar cells, such as solar cells having a surface areaof less than 1 cm², less than 0.1 cm² or even less than 0.05 cm² or 0.01cm². For example, substantially rectangular—such as square—solar cellscan be obtained in which the sides are less than 10, 5, 3, 2, 1 or even0.5 mm long. This makes it possible to obtain rectangular solar cellsout of a substantially circular wafer with a small waste of wafermaterial, whereas the approach of the disclosure makes it possible toeasily place an interconnect a large number of said solar cells inparallel, so that they, in combination, perform as a larger solar cell.

A further aspect of the disclosure related to a method for forming asolar cell assembly comprising a plurality of solar cells on a support,the method of comprising the steps of:

providing a support with a first side and an opposing second side, thesupport having a first conductive layer on the first side of thesupport, and a second conductive layer on the second side of thesuppoer, said conductive layers being separated by an insulating core;

establishing a plurality of vias through the support;

mounting a plurality of solar cells on the first side of the support,each solar cell of the plurality of solar cells comprising a top surfaceincluding a contact of a first polarity type (for example, a cathodecontact), and a rear surface including a contact of a second polaritytype (for example, an anode contact), so that the contact of secondpolarity type of each of the plurality of solar cells makes electricalcontact with the first conductive layer;

arranging a plurality of conductive interconnects so that eachrespective interconnect makes electrical contact with the contact of thefirst polarity type of a respective solar cell and extends through arespective via to make electrical contact with the second conductivelayer. In this way, solar cells can be packed close together on thefirst side of the support, and the first and the second metal layers canbe used to interconnect all of the solar cells in parallel.

In some embodiments of the disclosure, the method comprises removingconductive material on the first side of the support so as to establisha plurality of conductive strips. In some embodiment of the disclosure,the vias are arranged adjacent to the strips, for example, betweenadjacent strips. In some embodiments of the disclosure, the strips aregiven a shape, such as a substantially triangular shape, so that thewidth of the strip increases from a free end of the strip to a terminalend where the strip is electrically connected to other strips. Thisarrangement can sometimes be preferred to optimize the use of conductivematerial and minimize weight. In other embodiments of the disclosure,the strips have constant width.

In some embodiments of the disclosure, the method comprises removingconductive material on the second side of the support so as to establisha plurality of conductive strips. In some embodiment of the disclosure,the vias are arranged adjacent to the strips, for example, betweenadjacent strips. In some embodiments of the disclosure, the strips aregiven a shape, such as a substantially triangular shape, so that thewidth of the strip increases from a free end of the strip to a terminalend where the strip is electrically connected to other strips. Thisarrangement can sometimes be preferred to optimize the use of conductivematerial and minimize weight. In other embodiments of the disclosure,the strips have constant width. In some embodiments of the disclosure,the removal of conductive material is carried out so that conductivestrips are established having one free and being connected to each otherat an opposite end.

In some embodiments of the invention, the method comprises the step ofproviding a second terminal on the first side of the support and a firstterminal on the second side of the support, the first terminalcomprising a portion of the second conductive layer extending adjacent afirst edge of the support, and the second terminal comprisisng a portionof the first conductive layer extending adjacent to a second edge of thesupport, parallel with the first edge of the support. This canfacilitate the interconnection of a plurality of assemblies in serieswhen, for example, fabricating a solar array panel. For example, in someembodiments of the invention, the support is substantially rectangularand one solar cell assembly can be placed partially overlapping anotherone in correspondence with an edge, so that the first terminal of asecond one of the solar cell assemblies is placed on top of the secondterminal of the first solar cell assembly. Thereby, firm and reliablebonding and interconnection can be established without the use of anyadditional interconnects: the bonding can take place directly, using,for example, a suitable conductive soldering or welding material, suchas an indium alloy, to attach the respective first and second terminalsto each other. Thereby, a series of modules can be interconnected inseries in a simple and reliable manner, so that a desired output voltageis obtained, and each solar cell assembly includes a substantial amountof solar cells connected in parallel, so as to establish a desired levelof output current.

In some embodiments of the disclosure, the method comprises the step ofproviding a bypass diode on the assembly, in parallel with the solarcells. In some embodiments of the disclosure, the bypass diode ismounted on the first conductive layer and connected to the secondconductive layer through a via in the support, and in other embodimentsof the disclosure the bypass diode is mounted on the second conductivelayer and connected to the first conductive layer through a via in thesupport. In some embodiments, more than one bypass diode is provided oneach solar cell assembly.

In some embodiments of the disclosure, the method comprises the step ofobtaining at least a plurality of the solar cells by dividing, forexample cutting, at least one solar cell wafer into at least 10substantially square or rectangular solar cells, such as into at least100 or into at least 500 solar cells or more. In some embodiments of thedisclosure, after dividing said at least one solar cell wafer into aplurality of substantially square or rectangular solar cells, some ofsaid solar cells are selected so as not to be used for producing thesolar cell assembly; the solar cells selected not to be used forproducing the solar cell assembly may correspond to a defective regionof the solar cell wafer. Thereby, overall efficiency of the solar cellassembly is enhanced.

In some embodiments of the disclosure, the solar cells have a surfacearea of less than 5 cm², or in some embodiments less than 1 cm², lessthan 0.1 cm², less than 0.05 cm², or less than 0.01 cm². For example,substantially rectangular—such as square—solar cells can be obtained inwhich the sides are less than 10, 5, 3, 2, 1 or even 0.5 mm long.

In some embodiments of the disclosure, the conductive interconnects arewires, and in some embodiments of the disclosure the method compriseswire ball bonding the wires to the contacts of the first polarity typeand/or to the second conductive layer.

In some embodiments of the disclosure, the solar cells are III-Vcompound semiconductor multijunction solar cells. Such solar cellsfeature high efficiency but are relatively costly to manufacture. Thus,the reduced waste obtained by subdividing wafers into small solar cellsis beneficial from a cost perspective. Also, the use of small solarcells can be advantageous to enhance flexibility of the solar cellassemblies.

In some embodiments of the disclosure, the solar cells are attached tothe first conductive layer using a conductive bonding material, forexample, an indium alloy. Advantages involved with the use of an indiumalloy have been explained above.

A further aspect of the disclosure relates to a solar array panelcomprising a plurality of solar cell assemblies including at least afirst solar cell assembly and a second solar cell assembly, each solarcell assembly comprising a support having a first side and an opposingsecond side, with a first conductive layer disposed on the first side ofthe support and a second conductive layer disposed on the second side ofthe support, and a plurality of solar cells mounted on the first side ofthe support;

wherein the first solar cell assembly and the second solar cell assemblyare connected in series, wherein the second solar cell assemblypartially overlaps with the first solar cell assembly so that a portionof the second conductive layer of the second solar cell assemblyoverlaps with and is bonded to a portion of the first conductive layerof the first solar cell assembly. Thus, electrical series connectionbetween the first solar cell assembly and the second solar cell assemblycan be established by bonding the respective second and first layers toeach other where the assemblies overlap. Thus, a direct and reliableconnection can be established, without need for any additionalinterconnects. Two or more, such as three, four, five, ten, or moremodules or assemblies can be connected in series, and the connectionscan be established without use of additional and/or complexinterconnects. The direct connection can serve to simplify themanufacturing and facilitate automation thereof. In addition, as theinterconnection can be established at a plurality of points along andacross the overlapping portions, and/or over a substantial portion ofthe overlapping surface, the interconnection can be established in avery reliable manner, using welding or soldering techniques and, ifdesired, additional conductive bonding material that is placed betweenthe overlapping portions and melted during the welding or solderingprocess. In some embodiments of the invention, an indium alloy can beused as a bonding material. Thus, solar cell assemblies or modules canbe placed one after the other so as to form a solar array panelcomprising a plurality of said solar cell assemblies, arranged in one ormore strings of series connected solar cell assemblies, the solar cellassemblies within each string partly overlapping with each other, in amanner resembling the manner in which tiles are often arranged on theroofs of buildings, etc.

In some embodiments of the disclosure, the solar cell assemblies areflexible. Thus, when the solar cell assemblies are arranged on asubstrate with a second solar cell assembly partly overlapping with afirst solar cell assembly, the second solar cell assembly can, due toits flexibility, adapt so that part of it extends in parallel with thefirst solar cell assembly, that is, along a top surface of thesubstrate, whereas another part of it is curved so that it extendsupwards from the substrate in the vicinity of an edge of the first solarcell assembly, and overlies a portion of the first solar cell assemblyin the vicinity of said edge. Thus, in some embodiments of thedisclosure, the solar cell assemblies are placed so that at least asecond solar cell assembly partially overlaps at least a first solarcell assembly, whereby the second solar cell assembly adapts it shapeaccordingly, whereby part of the second solar cell assembly and at leastpart of the first solar cell assembly are arranged in one plane, and atleast another part of the second solar cell assembly is arranged in adifferent plane, parallel with the first plane.

In some embodiments of the disclosure, the solar cells are distributedover a first portion of the first surface of each solar cell assembly,and a second portion of the first surface is free from solar cells, andthe second solar cell assembly overlaps with the first solar cellassembly in correspondence with the second portion of the first surfaceof the first solar cell assembly. The first portion is preferablysubstantially larger than the second portion. For example, the firstportion is preferably at least five times larger than the secondportion, preferably at least ten times larger.

In some embodiments of the disclosure, each solar cell assemblycomprises a first terminal comprising a conductive region on the secondside of the support adjacent a first edge of the support, and a secondterminal comprising a conductive region on the first side of the supportadjacent a second edge of the support, opposite said first edge of thesupport. That is, the support can have a substantially rectangularshape, and the terminals can be arranged in correspondence with, thatis, adjacent to opposite peripheral edges of the support and on oppositesides of the support. One or both of said terminals can correspond to apart of the corresponding conductive layer extending in parallel withand adjacent to the corresponding edge. Thereby, the solar cellassemblies can easily be arranged in a string, in a partly overlappingmanner, so that the first terminal of the second solar cell assembly isplaced on top of and in contact with the second terminal of the firstsolar cell assembly, and so on.

In some embodiments of the disclosure, the solar cells on each solarcell assembly are connected in parallel. Thus, each solar cell assemblycan include an appropriate amount of solar cells so as to produce, whenin use, a desired amount of output current. The voltage level can bedetermined by choosing the number of solar cell assemblies that areconnected in series in each string.

In some embodiments of the disclosure, each solar cell comprises a topsurface including a contact of a first polarity type, and a rear surfaceincluding a contact of a second polarity type, the contact of secondpolarity type of each of the plurality of solar cells making electricalcontact with the first conductive layer and the contact of the firstpolarity type of each of the plurality of solar cells being electricallyconnected to the second conductive layer. Thus, the arrangement with twoconductive layers on opposite sides of the substrate serves on the onehand to connect the solar cells on the module in parallel, and on theother hand to provide for a simple and reliable interconnection of aplurality of solar cell assemblies or modules in series, in thepartially overlapping manner described above.

In some embodiments of the disclosure, each solar cell assemblycomprises a plurality of vias in the support extending from the firstside of the support to the second side of the support, and a pluralityof conductive interconnects extend from the first side of the support tothe second side of the support, each respective interconnect makingelectrical contact with the contact of the first polarity type of arespective solar cell and extending through a respective via to makeelectrical contact with the second conductive layer disposed on thesecond side of the support. That is, the solar cells arranged on thefirst side of the support and connected to the first conductive layervia their rear contacts, are connected to the second conductive layervia interconnects, such as wires, passing through respective vias in thesupport.

In some embodiments of the disclosure, the first conductive layercomprises a plurality of strips, such as substantially rectangular ortriangular strips, extending across the first side of the support. Insome embodiments of the disclosure, each strip has a free end adjacentto one edge of the support, and another end where the strip is connectedto a part of the conductive layer that extends along another edge of thesupport and which constitutes or forms part of the second terminal. Inthe embodiments in which vias are present in the support, the vias canbe arranged in parallel with the strips, between adjacent strips. Thesolar cell assemblies can be arranged on a substrate, glued to thesubstrate.

In some embodiments of the disclosure, the solar cells have a surfacearea of less than 5 cm², or in some embodiments less than 1 cm², lessthan 0.1 cm², less than 0.05 cm², or less than 0.01 cm². For example,substantially rectangular—such as square—solar cells can be used inwhich the sides are less than 10, 5, 3, 2, 1 or even 0.5 mm long.

In some embodiments of the disclosure, the solar cells are III-Vcompound semiconductor multijunction solar cells. Such solar cellsfeature high efficiency but are relatively costly to manufacture. Thus,the solar array panel can comprise a plurality of series connectedmodules, each of which comprises a large amount of small solar cellsconnected in parallel. Errors in individual solar cells will notsubstantially affect the performance of the entire module, and themodules can be interconnected as described to provide for a reliableinterconnection, minimizing the risk for errors and enhancing thereliability of the performance of each string of modules.

A further aspect of the disclosure relates to a method of manufacturinga solar array panel, comprising the steps of:

providing a plurality of solar cell assemblies including at least afirst solar cell assembly and a second solar cell assembly, each solarcell assembly comprising a support having a first side and an opposingsecond side, with a first conductive layer disposed on the first side ofthe support and a second conductive layer disposed on the second side ofthe support, and a plurality of solar cells mounted on the first side ofthe support;

placing the first solar cell assembly on a substrate;

placing the second solar cell assembly on the substrate so that thesecond solar cell assembly partially overlaps with the first solar cellassembly so that a portion of the second conductive layer of the secondsolar cell assembly overlaps with a portion of the first conductivelayer of the first solar cell assembly;

bonding the portion of the second conductive layer to the portion of thefirst conductive layer, so as to establish a mechanical and electricalconnection between the two conductive layers. The connection can beestablished at one or more specific points or areas of the overlap, forexample, along and across the entire overlap or most of it, or only atspecific points. The way in which the bonding is carried out can beselected to optimize the performance in terms of, for example,simplicity of manufacture, reliability of the electrical and/ormechanical connection, flexibility of the panel, etc.

The step of attaching the two portions to each other can, for example,include the step of applying heat and/or pressure. In some embodimentsof the invention, a conductive soldering material is applied in the areaof the overlap, for example, on the portion of the first conductivelayer or on the portion of the second conductive layer, prior tobringing the two portions in contact with each other.

In some embodiments of the disclosure, the method comprises the step ofapplying a conductive soldering material onto a portion of the firstconductive layer in correspondence with an edge of the first solar cellassembly, prior to placing the second solar cell assembly onto thestructure.

In some embodiments of the disclosure, the solar cell assemblies areplaced on the structure using at least one pick-and-place device.

In some embodiments of the disclosure, the supports are flexible so thatthe solar cell assemblies adapt their shape when placed on thestructure, so that, for example, when the second solar cell assembly isplaced on the structure partially overlapping with the first solar cellassembly, its shape is adapted so that, for example, a major portion ofthe second solar cell assembly is arranged on the structure and coplanarwith a major portion of the first solar cell assembly, whereas a minorportion of the second solar cell assembly extends upwards from saidstructure and over a portion of the first solar cell assembly, incorrespondence with an edge of the first solar cell assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

To complete the description and in order to provide for a betterunderstanding of the disclosure, a set of drawings is provided. Saiddrawings form an integral part of the description and illustrateembodiments of the disclosure, which should not be interpreted asrestricting the scope of the disclosure, but just as examples of how thedisclosure can be carried out. The drawings comprise the followingfigures:

FIG. 1 is a perspective view of a support that can be used forfabricating a module according to the present disclosure depictingmetallization over the top and bottom surfaces;

FIG. 2A is a perspective view of the support of FIG. 1 after a step offorming a plurality of grooves in a top metal layer of the support in afirst embodiment;

FIG. 2B is a perspective view of the support of FIG. 1 after a step offorming a plurality of grooves in the top metal layer of the support ina second embodiment;

FIG. 3A is a top plan view of the support of FIG. 2A in a firstembodiment;

FIG. 3B is a bottom perspective view of the support of FIG. 2A in afirst embodiment;

FIG. 3C is a bottom perspective view of the support of FIG. 2A in asecond embodiment;

FIG. 4A is a top plan view of the support of FIG. 3A after the nextprocess step of providing vias extending into or through the supportaccording to the present disclosure;

FIG. 4B is a cross-sectional view of the support of FIG. 4A through the4B-4B plane in FIG. 4A;

FIG. 4C is a bottom perspective view of the support of FIG. 4A in firstembodiment;

FIG. 4D is a cross-sectional view of the support according to thepresent disclosure in a second embodiment;

FIG. 4E is a bottom perspective view of the support of FIG. 4D in asecond embodiment;

FIG. 4F is a bottom perspective view of the support of FIG. 4A in asecond embodiment;

FIG. 4G is a bottom perspective view of the support of FIG. 4A in asecond embodiment;

FIG. 5A is a perspective view of the support of FIG. 4A after the nextprocess step of mounting a plurality of solar cells on the first stripaccording to the present disclosure;

FIG. 5B is a cross-sectional view of the support of FIG. 5A through the5B-5B plane shown in FIG. 5A;

FIG. 5C is a cross-sectional view of the support of FIG. 5A through the5C-5C plane shown in FIG. 5A;

FIG. 5D is a perspective view of the support of FIG. 4A after the nextprocess step according to the present disclosure of mounting a pluralityof solar cells on the second strip;

FIG. 6A is a perspective view of the support of FIG. 5A after the nextprocess step of attaching an interconnect to each of the plurality ofsolar cells and passing each interconnect through an adjoiningrespective via according to the present disclosure;

FIG. 6B is a cross-sectional view of the support of FIG. 5A through the6B-6B plane shown in FIG. 5A in a first embodiment;

FIG. 6C is a cross-sectional view of the support of FIG. 6A through the6C-6C plane shown in FIG. 6A depicting the interconnect arrangement inthe first embodiment according to the present disclosure;

FIG. 6D is a bottom view of the support of FIG. 6A in which theinterconnect extending through a respective via is electricallyconnected to a portion of the metallization layer on the back surface;

FIG. 6E is a schematic diagram of the components of the module of FIG.6A;

FIG. 6F is a cross-sectional view of the support of FIG. 5A through the6B-6B plane shown in FIG. 5A in a second embodiment according to thepresent disclosure;

FIG. 6G is a cross-sectional view of the support of FIG. 6A depictingthe interconnect arrangement in the second embodiment according to thepresent disclosure in which the interconnect extends through arespective via and is electrically connected to a portion of themetallization layer on the back surface at the bottom of the via;

FIG. 7A is a schematic cross-sectional view of a first solar cell moduleof FIG. 6A mounted on a panel or supporting substrate during the firststep of a panel assembly process;

FIG. 7B is a schematic cross-sectional view of a second solar cellmodule of FIG. 6A positioned and about to be coupled with the firstsolar cell module during the second step of a panel assembly process;

FIG. 7C is a schematic cross-sectional view of the second solar cellmodule shown in FIG. 7B being coupled with the first solar cell moduleshown in FIG. 7A during the third step of a panel assembly process;

FIG. 7D is a schematic cross-sectional view of the second solar cellmodule shown in FIG. 7C being mounted on the panel or supportingsubstrate during the fourth step of a panel assembly process; and

FIG. 8 is a highly simplified perspective view of a space vehicleincorporating an array in which the deployable solar cell panelincorporates the interconnected solar cell module assemblies accordingto the present disclosure.

DETAILED DESCRIPTION

Details of the present disclosure will now be described includingexemplary aspects and embodiments thereof. Referring to the drawings andthe following description, like reference numbers are used to identifylike or functionally similar elements, and are intended to illustratemajor features of exemplary embodiments in a highly simplifieddiagrammatic manner. Moreover, the drawings are not intended to depictevery feature of the actual embodiment nor the relative dimensions ofthe depicted elements, and are not drawn to scale.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, theappearances of the phrases “in one embodiment” or “in an embodiment” invarious places throughout this specification are not necessarily allreferring to the same embodiment. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more embodiments.

The present disclosure provides a process for the design and fabricationof a modular solar cell subassembly, and the fabrication of a solar cellarray panel utilizing such interconnected modular subassemblies.

FIG. 1 illustrates an example of a support 100 that can be used in anembodiment of the disclosure in the fabrication of the modularsubassembly. The support comprises an insulating support layer 101 and aconductive metal layer 102 arranged on a top surface of the supportlayer 101 and a conductive metal layer 103 arranged on a bottom surfaceof the support layer 101. In some embodiments of the disclosure, themetal layer 102 is a copper layer, having a thickness in the range offrom 1 μm and up to 50 μm. In some embodiments of the disclosure, thesupport layer 101 is a KAPTON® sheet. The chemical name for KAPTON® ispoly (4,4′-oxydiphenylene-pyromellitimide). A polyimide film sheet orlayer may also be used. Preferably the metal layer is attached to thesupport layer in an adhesive-less manner, to limit outgassing when usedin a space environment. In some embodiments of the disclosure thesupport layer can have a thickness in the range of 1 mil (25.4 μm) to 4mil (101.6 μm). In some embodiments of the disclosure, a support can beprovided comprising KAPTON®, or another suitable support material, onboth sides of the metal film 102, with cut-outs for the attachment ofsolar cells and interconnects to the metal film. In some embodiments ofthe disclosure, the metal film layer 103 at the bottom surface of thesupport is of the same material and has the same or a similar thicknessas the metal film layer 102 at the top surface of the support. In someembodiments, the two metal film layers are of different materials and/orhave different thicknesses.

Although the support 100 is depicted in FIG. 1 as the size and shape ofthe ultimate module, which may be a square or rectangular elementranging from 1 inch to 6 inches on a side, the support 100 may befabricated out of a roll or larger support material such as a polymidefilm which is automatically processed and cut to produce the individualsupport 100 depicted in FIG. 1, or subsequently depicted processedstructures in FIG. 2 through 4. A description of such fabricationprocesses goes beyond the scope of the present disclosure.

FIG. 2A is a perspective view of the support 100 of FIG. 1 after a stepof forming a plurality of grooves in a top metal layer of the support ina first embodiment. FIG. 2A illustrates the support 100 of FIG. 1 aftera step in which a portion of the metal layer 102 has been removed, byfor example etching or laser scribing, whereby channels or grooves 105a, 106 a, . . . 111 a are formed traversing the metal layer 102,separating it into at least a plurality of strips 105, 106, . . . 112extending in parallel and in some embodiments connected to each other ata terminal 120 on a perpetual edge of the support 100.

FIG. 2B is a perspective view of the support 100 of FIG. 1 after a stepof forming a plurality of grooves 180 a, 181 a, 182 a, . . . etc. andmetal strips 180, 181, . . . etc. in the top metal layer of the supportin a second embodiment. Here, the grooves 180 a, 181 a etc. are V-shapedor triangular, and so are the strips 180, 181, . . . 187. The use ofthis kind of strips the width of which increases along the strip whenmoving from the free end of the strip to the end where the strip isconnected to the band or second terminal 120, is that when in use andwith solar cells arranged in a row along the strip 180, current willflow in one direction, and the current will be lowest towards the freeend of the strip (where the current corresponds to the one produced byone solar cell), and higher towards the end where the strip connects tothe terminal 120 (where the current is the sum of the currents producedby the solar cells arranged on the strip). Thus, the need for asufficient cross section of conductive material is higher towards theend where the strip mates with the second terminal 120. Thus, theincreasing width corresponds to an optimization of the use of conductivematerial, which can be important especially for space applications.

FIG. 3A is a top plan view of the support 100 of FIG. 2A in a firstembodiment with strips 105, 106, . . . 112 extending along the topsurface.

FIG. 3B is a bottom plan view of the support 100 of FIG. 2A in a firstembodiment. Here, the bottom metal layer 103 completely covers thebottom surface of the support 100.

FIG. 3C is a bottom plan view of the support of FIG. 2A in a secondembodiment. Here, triangular grooves 130 a, 131 a, . . . 136 a have beenestablished, separating triangular strips 130, 131, . . . 137. The widthof the strips increases towards the end where the strips are connectedto the first terminal 139. The advantages involved with this areanalogous to the ones described above in relation to the V-shaped stripsat the top surface in the embodiment shown in FIG. 2B.

FIG. 4A is a top plan view of the support of FIG. 3A after the nextprocess step of providing vias 146, 147 along groove 105 a, and vias246, 277 along groove 106 a, etc. extending into or through the support100 according to the present disclosure. The vias can be provided usingany suitable means and in one embodiment may be provided in layer 101prior to metallization of the layers 102, 103.

FIG. 4B is a cross-sectional view of the support of FIG. 4A through the4B-4B plane in FIG. 4A and illustrates in the first embodiment how thevias 140, 141, . . . 147 traverse the support 101 and the metal filmlayer 103 on the bottom of the support 101.

FIG. 4C is a bottom plan view of the support of FIG. 4A in firstembodiment and illustrates how the vias 140, 141, . . . 147 traverse themetal film layer 103 and emerge at the bottom surface thereof (Only onerow of vias 140, . . . 147 are shown for simplicity).

FIG. 4D is a cross-sectional view of the support of FIG. 4A according tothe present disclosure in a second embodiment in which the vias 140,141, . . . 147 traverse the support 101 and stop at the top of the metalfilm layer which we designate in this embodiment by 103 a. In thissecond embodiment, the metal film layer is designated as 103 a todistinguish it from the metal film layer 103 of the first embodiment.

FIG. 4E is a bottom perspective view of the support of FIG. 4D in thesecond embodiment depicting the metal film layer 103 a covering theentire bottom surface.

FIG. 4F is a bottom plan view of the support of FIG. 4A is a variationof the embodiment of FIG. 4C, but here the metal film layer 103 isformed into triangular strips 130, 131, . . . 137. Here, the vias 140,141, . . . 147 are arranged in the grooves 130 a, 131 a, etc.

FIG. 4G is a bottom perspective view of the support of FIG. 4A in asecond embodiment as a variation of the embodiment of FIG. 4E in whichthe vias 140, 141, . . . 147 traverse the support 101 and stop at thetop of the metal film layer 103 a, at strips 130, 131, . . . 137.

FIG. 5A is a perspective view of the support of FIG. 4A after the nextprocess step of mounting a plurality of solar cells 200, 201, . . . 207on a first one 105 of the strips according to the present disclosure.Each solar cell has a top surface in which a contact pad (in theenlarged depiction represented by 207 a for solar cell 207), such as acathode contact pad, is provided. FIG. 5A schematically illustrates howa plurality of solar cells 200, 201 . . . etc. have been electricallyconnected to one of the strips forming part of the first conductiveportion. The solar cells 200, 201, . . . 207 are preferably placed closeto each other (from 0.1 to 1 mm apart or other suitable spacing that maybe possible using standard “pick-and-place” fabrication equipment) andall throughout the strips, so as to optimize space utilization. In FIGS.5B and 5C the solar cells are shown separated by a small gap or space250, 251, . . . etc. It is preferred that a substantial percentage, suchas more than 50%, 60%, 70%, 80% or 90%, such as more than 95%, of thetop surface support 101 is covered by solar cells, so as to provide anoptimized W/m² or W/kg ratio. However, a portion of the top metal layer,such as the terminal 120 extending along a peripheral edge of thesupport, can be left free of solar cells, and serve to establish directseries or parallel connection with an adjacent solar cell assembly ormodule.

Each solar cell 200, 201, . . . etc. comprises a bottom contact 210 on arear or bottom surface of the solar cell, as shown in FIG. 6B for solarcell 207, and a top contact 207 a on a front or top surface of the solarcell 207. In some embodiments of the disclosure, the bottom contact 210comprises a metal layer covering the entire rear surface of the solarcell or a substantial portion of the rear surface of the solar cell, andthe top contact 207 a is a small pad placed adjacent to an edge of thefront surface of the solar cell 207. The top contact 207 a haspreferably a small surface area to allow the major part of the frontsurface of the solar cell to be an effective surface for the conversionof sunlight into electric power. In the enlarged portion of FIG. 5A, thetop contact 207 a is only shown for one of the solar cells 207, forsimplicity.

The solar cell 207 is preferably attached to the metal strip 105 by aconductive bonding material 211 as shown in FIG. 6B, such as a layer ofa metal alloy, such as an indium alloy, such as an indium lead alloy. Asis easily understood from FIG. 6B and FIG. 6C, the metal layer includingthe strip 105 serves as a heat sink for the solar cells, and an indiumalloy such as indium lead has appropriate heat conductioncharacteristics. At the same time, indium is advantageous as it providesfor ductility, thereby reducing the risk for cracks in the bonds betweenthe solar cells and the metal strip 105 when the assembly is subjectedto the bending forces.

FIG. 5B is a cross-sectional view of the support of FIG. 5A through the5B-5B plane shown in FIG. 5A.

FIG. 5C is a cross-sectional view of the support of FIG. 5A through the5C-5C plane shown in FIG. 5A.

FIG. 5D is a perspective view of the support of FIG. 4A after the nextprocess step according to the present disclosure of mounting a pluralityof solar cells 300, . . . 307 on the second strip 106. The completepopulation of all strips 105, 106, . . . 112 with solar cells is notshown for simplicity of the drawing.

FIG. 6A is a perspective view of the support of FIG. 5A after the nextprocess step of attaching an interconnect 400 to each of the pluralityof solar cells and passing each interconnect through an adjoiningrespective via according to the present disclosure. In this embodiment,the interconnect is a simple wire 400. Wire bonding can be used toattach the wire to the contact pad at the top surface of the solar cell,using standard wire bonding techniques and standard automation equipmentfor wire bonding.

FIG. 6B which has already been discussed above is a cross-sectional viewof the support of FIG. 6A through the 6B-6B plane shown in FIG. 5A, andshows the corresponding part of the assembly prior to incorporation ofthe wire including the channel 105 a shown in FIG. 2A and the via 147.

FIG. 6C is a cross-sectional view of the support of FIG. 6A through the6C-6C plane shown in FIG. 6A and illustrates the same part of theassembly after incorporation of the wire 400 in a first embodiment.Here, it can be seen how the wire 400 interconnects the contact pad 201and the metal layer 103 on the bottom surface of the support. A firstend 401 of the wire is wire bonded to the contact pad 207 a, and asecond end 403 of the wire is wire bonded to the bottom surface of themetal layer 103, and the first end 401 and the second end 403 areinterconnected by a portion 402 of the wire that extends through the via147.

FIG. 6D is a bottom view of the support of FIG. 6A in which theinterconnects 400 extending through a respective via 740, . . . 747along the groove 137 a is electrically connected to a portion, namely,to a triangular strip 137 of the metallization layer 103 on the backsurface. It should be observed that FIGS. 6A-6D are purely schematic andthat in practice, in other embodiments the interconnects 400 may notprotrude beyond the bottom surface of the support as shown in FIG. 6D,as will be presented in FIGS. 6F and 6G below.

FIG. 6E is a schematic diagram of the components of the first row ofsolar cells 200, . . . 207 in the module of FIG. 6A, and shows how aplurality of such solar cells are connected in parallel due to theirconnection to the top conductive layer 102 and the bottom conductivelayer 103. In addition, a bypass diode 350 is connected in parallel withthe row of solar cells, also by connection to the top conductive layer102 and the bottom conductive layer 103. The diode 350 can be physicallyimplemented on any of the two sides of the support. For example, in someembodiments, the bypass diode can be placed on the same side of thesupport as the solar cells, for example, adjoining one or more of thesolar cells 200 shown in FIG. 6A. In other embodiments, the diode can beimplemented on the bottom side of the support. Depictions of the diode350 are not shown in the other figures for simplicity of the drawings.

FIG. 6F is a cross-sectional view of the support of FIG. 5A through the6B-6B plane shown in FIG. 5A in a second embodiment according to thepresent disclosure.

FIG. 6G is a cross-sectional view of the support of FIG. 6A depictingthe interconnect arrangement in the embodiment according to the presentdisclosure in which the interconnect 400 extends through a respectivevia 160 and is electrically connected at the end 403 of the interconnect400 to a portion 161 of the top surface of the metallization layer 103 adisposed at the bottom of the via 160.

It is clear from the embodiments schematically shown in the figuresdiscussed above how many small solar cells, such as solar cells having asurface area of less than 1 cm², less than 0.1 cm² or less than 0.01cm², can easily be placed on the first conductive portion such as ondifferent subareas, tracks or strips of the first conductive portion,and bonded to it by bonding their back sides to the first conductiveportion using a conductive bond that connects that bottom contact of thesolar cell to the first conductive layer 102, and how interconnects 400can be added to connect the top contacts of the solar cells to thesecond conductive layer 103, through vias 150 through the support. Oneor more bypass diodes can easily be added, as explained.

Thus, an assembly of a plurality of solar cells connected in parallel isobtained, and this kind of assembly can be used as a subassembly ormodule, together with more subassemblies or modules of the same kind, toform a larger assembly, such as a solar array panel, including stringsof series connected assemblies.

Although a parallel electrical interconnection scheme is the specificarrangement depicted in the present disclosure, the interconnection ofindividual solar cells in a module by suitable arrangements or tracepatterns of the conductive layers on the first and second sides of thesupport.

The figures are only intended to schematically show embodiments of thedisclosure. In practice, the spatial distribution will mostly differ:solar cells are to be packed relatively close to each other and arrangedto occupy most of the surface of the assembly, so as to contribute to anefficient space utilization from a W/m² perspective.

FIG. 7A is a schematic cross-sectional view of a first solar cell moduleor assembly 1000 of the type described above, mounted on a panel orsupporting substrate 500 during the first step of a panel assemblyprocess. An adhesive layer 501 is present on the top surface of thesubstrate 500 for attaching the assembly 1000 to the substrate 500. Ainterconnection pad 550, for example, of a conductive material—such asfor example an indium alloy—that can be fused to bond two conductivelayers to each other, is placed adjacent to an edge of the assembly1000, on top of the first conductive layer 102 and, more specifically,on the second terminal part of the first conductive layer.

FIG. 7B schematically illustrates how a second solar cell assembly 1001,of the same type as the first solar cell assembly 1000, is beingtransferred to a position partially overlapping with the first solarcell assembly 1000, by a schematically illustrated pick-and-placeapparatus 502.

FIG. 7C schematically illustrates a third step of the process, with thesecond solar cell module 1001 coupled with the first solar cell module1000. It can be seen how the second solar cell module 1001 and the firstsolar cell module partially overlap with each other: more specifically,the second solar cell module 1001 is placed on top of a portion of thefirst conductive layer 102 of the first solar cell module 1000 that isfree from solar cells, that is, a portion that corresponds to the secondterminal described above.

FIG. 7D schematically illustrates the first and the second solar cellmodules arranged on the supporting substrate after a fourth step of apanel assembly process. Here, a major portion of the second solar cellassembly 1001 has been aligned with the first solar cell assembly 1000and glued to the supporting substrate 500 by the adhesive layer 501. Thefirst terminal of the second solar cell assembly 1001 has been bonded tothe second terminal of the first solar cell assembly 1000.

FIG. 8 is a highly simplified perspective view of a space vehicle 10000incorporating a solar cell array 2000 in the form of a deployableflexible sheet including a flexible substrate 500 on which solar cellmodules 1000 and 1001 according to the present disclosure are placed.The sheet may wrap around a mandrel 2001 prior to being deployed inspace. The space vehicle 10000 includes a payload 10003 which is poweredby the array of solar cell assemblies 2000.

It is to be noted that the terms “front”, “back”, “top”, “bottom”,“over”, “on”, “under”, and the like in the description and in theclaims, if any, are used for descriptive purposes and not necessarilyfor describing permanent relative positions. It is understood that theterms so used are interchangeable under appropriate circumstances suchthat the embodiments of the disclosure described herein are, forexample, capable of operation in other orientations than thoseillustrated or otherwise described herein.

Furthermore, those skilled in the art will recognize that boundariesbetween the above described operations are merely illustrative. Themultiple units/operations may be combined into a single unit/operation,a single unit/operation may be distributed in additionalunits/operations, and units/operations may be operated at leastpartially overlapping in time. Moreover, alternative embodiments mayinclude multiple instances of a particular unit/operation, and the orderof operations may be altered in various other embodiments.

In the claims, the word ‘comprising’ or ‘having’ does not exclude thepresence of other elements or steps than those listed in a claims. Theterms “a” or “an”, as used herein, are defined as one or more than one.Also, the use of introductory phrases such as “at least one” and “one ormore” in the claims should not be construed to imply that theintroduction of another claim element by the indefinite articles “a” or“an” limits any particular claim containing such introduced claimelement to disclosures containing only one such element, even when theclaim includes the introductory phrases “one or more” or “at least one”and indefinite articles such as “a” or “an”. The same holds true for theuse of definite articles. Unless stated otherwise, terms such as “first”and “second” are used to arbitrarily distinguish between the elementssuch terms describe. Thus, these terms are not necessarily intended toindicate temporal or other prioritization of such elements. The factthat certain measures are recited in mutually different claims does notindicate that a combination of these measures cannot be used toadvantage.

The present disclosure can be embodied in various ways. The abovedescribed orders of the steps for the methods are only intended to beillustrative, and the steps of the methods of the present disclosure arenot limited to the above specifically described orders unless otherwisespecifically stated. Note that the embodiments of the present disclosurecan be freely combined with each other without departing from the spiritand scope of the disclosure.

Although some specific embodiments of the present disclosure have beendemonstrated in detail with examples, it should be understood by aperson skilled in the art that the above examples are only intended tobe illustrative but not to limit the scope of the present disclosure. Itshould be understood that the above embodiments can be modified withoutdeparting from the scope and spirit of the present disclosure which areto be defined by the attached claims.

The invention claimed is:
 1. A solar assembly comprising: a supportcomprising a first side and an opposing second side, wherein the supportis electrically insulating; a first terminal disposed on the second sideof the support a first conductive layer disposed on the first side ofthe support, the first conductive layer comprising a second terminal anda first plurality of strips extending away from the second terminal andhaving a thickness in the range of 5 to 50 microns; a second conductivelayer disposed on the second side of the support, such that the firstand second conductive layers are not coplanar; a plurality of solarcells organized into subsets of more than one solar cell and with eachsubset being mounted on a strip of the first plurality of strips, eachsolar cell of the plurality of solar cells comprising a top surfaceincluding a contact of a first polarity type, and a rear surfaceincluding a contact of a second polarity type, the contact of secondpolarity type of each of the plurality of solar cells making electricalcontact with the first conductive layer; and a plurality of conductiveinterconnects extending from the first side of the support to the secondconductive layer, each respective interconnect making electrical contactwith the contact of the first polarity type of a respective solar celland extending through a respective via disposed in and extending throughthe support between the opposing sides to make electrical contact withthe second conductive layer disposed on the second side of the support;and wherein each strip of the first plurality of strips extends beyond aperiphery of the solar cells of the subset mounted thereon, such thatthe solar cells of the subset mounted thereon electrical contact withthe second terminal and are connected in parallel through the secondterminal.
 2. A solar cell assembly as defined in claim 1, wherein eachstrip of the first plurality of strips has a width that increases from afree end of the strip to an end of the strip where the strip iselectrically connected to the second terminal.
 3. A solar cell assemblyas defined in claim 1, wherein each of the solar cells has a dimensionin the range of 5 to 10 mm on a side.
 4. A solar cell assembly asdefined in claim 1, wherein the second conductive layer comprises asecond plurality of strips, wherein each strip of the second pluralityof strips has a width that increases from a free end of the strip to anend of the strip where the strip is electrically connected to the firstterminal.
 5. A solar cell assembly as defined in claim 1, wherein thesupport is a polyimide film having a thickness of between 25 and 100microns.
 6. A solar cell assembly as defined in claim 1, wherein theconductive interconnects comprise a wire extending from and ball bondedto the contact of first polarity type of one of the solar cells to thebottom surface of the support through the respective via, wherein eachof the vias has a diameter of between 100 and 200 microns.
 7. A solarcell assembly as defined in claim 1, wherein the first terminal of thesolar cell assembly is disposed on a first peripheral edge of the solarcell assembly, wherein the second terminal of the solar cell assembly iscomposed of a metallic strip extending parallel to the first peripheraledge of the solar cell assembly.
 8. A solar cell assembly as defined inclaim 1, further comprising a bypass diode electrically mounted inparallel with the solar cells and functioning as a bypass diode of thesolar cell assembly, wherein the bypass diode has a top terminal of afirst conductivity type and a bottom terminal of a second conductivitytype, and the bottom terminal is mounted on and electrically connectedto the first conductive layer.
 9. A solar cell assembly as defined inclaim 1, wherein the solar cells are discrete multijunction III/Vcompound semiconductor solar cells, wherein the solar cells are arrangedin an array on the first side of the support comprising not less than 9and not more than 36 solar cells.
 10. A solar array panel comprising aplurality of modular solar cell assemblies, each solar cell assemblyincluding an interconnect which electrically and mechanically connectsthe solar cell assembly with an adjacent solar cell assembly, andwherein each solar cell assembly comprises: a support comprising a firstside and an opposing second side, wherein the support is electricallyinsulating; a first terminal disposed on the second side of the supporta first conductive layer disposed on the first side of the support, thefirst conductive layer comprising a second terminal and a firstplurality of strips extending away from the second terminal and having athickness in the range of 5 to 50 microns; a second conductive layerdisposed on the second side of the support, such that the first andsecond conductive layers are not coplanar; a plurality of solar cells,organized into subsets of more than one solar cell and with each subsetbeing mounted on a strip of the first plurality of strips, each solarcell of the plurality of solar cells comprising a top surface includinga contact of first polarity type, and a rear surface including a contactof the second polarity type, the contact of second polarity type of eachof the plurality of solar cells making electrical contact with thesecond terminal of the first conductive layer, wherein the firstconductive layer comprised of the second terminal extends beyond aperiphery of each of the plurality of solar cells; and a plurality ofconductive interconnects extending from the first side of the support tothe second conductive layer, each respective interconnect makingelectrical contact with the contact of the first polarity type of arespective solar cell and extending through a respective via to makeelectrical contact with the second conductive layer disposed on thesecond side of the support; wherein each strip of the first plurality ofstrips extends beyond a periphery of the solar cells of the subsetmounted thereon, such that the solar cells of the subset mounted thereonmake electrical contact with the second terminal and are connected inparallel through the second terminal, and wherein at least two modularsolar cell assemblies are stacked in a partially overlappingconfiguration so that the first terminal of a second solar cell assemblyis placed on top of the second terminal of a first solar cell assemblyand an electrical connection is made between the respective first andsecond terminals of the stacked solar cell assemblies.
 11. A solar cellassembly as defined in claim 1, wherein the vias are arranged betweenadjacent strips of the first plurality of strips of the first conductivelayer.
 12. A solar array panel as defined in claim 10, wherein the viasare arranged between adjacent strips of the plurality of parallel stripsof the first conductive layer.
 13. A solar cell assembly as defined inclaim 1, wherein the first conductive layer comprises a plurality ofparallel strips of equal width.
 14. A solar array panel as defined inclaim 10, wherein the first plurality of strips are parallel and ofequal width.
 15. A solar cell assembly as defined in claim 1, whereinthe plurality of solar cells are electrically connected in series.
 16. Asolar cell assembly as defined in claim 1, wherein adjacent strips ofthe first conductive layer are separated by a groove and the viasthrough which the interconnects extend is positioned in the groove. 17.A solar cell assembly as defined in claim 1, wherein two or more solarcells are disposed adjacent to one another on each of strip of the firstplurality strips, wherein each of the solar cells has a dimension in therange of 5 to 10 mm on a side, wherein the support is a polyimide filmhaving a thickness of between 25 and 100 microns, wherein adjacentstrips of the plurality of strips of are separated by a groove and thevias through which the interconnects extend are positioned in thegroove, wherein the conductive interconnect comprises a wire extendingfrom and ball bonded to the contact of first polarity type to the bottomsurface of the support through the respective via, wherein the via has adiameter of between 100 and 200 microns, and wherein the solar cells arediscrete multijunction III/V compound semiconductor solar cells, whereinthe solar cells are arranged in an array on the first side of thesupport comprising not less than 9 and not more than 36 solar cells.